1. Field of the Invention
This invention relates to electronic circuit boards or cards and, more particularly, to electronic circuit cards in which heat pipe technology is used to dissipate heat therefrom.
2. Background of the Invention
In many electronic systems, particularly those carried in vehicles such as aircraft where high-density packaging prevails because of space limitations, the efficient cooling of electronic components has become a significant problem. With the advent of large-scale integrated circuit (IC) modules containing many thousands of circuit elements, it has become possible to pack great numbers of electronic components together within a very small volume. As is well known, these integrated circuit modules generate significant amounts of heat during the course of their normal operation. Since most solid state devices are sensitive to excessive temperatures, a solution to the problem of the generation of heat by large scale IC's in close proximity to one another has become of increasing concern to industry.
A typical approach to cooling components in electronic systems in which devices containing integrated circuits are placed on circuit cards is to direct a stream of cooling air across the modules and/or cards. One of the principal disadvantages of this approach is that the air quality (moisture content, contamination, etc.) must be tightly controlled to inhibit corrosion, loss of cooling effectiveness, etc. This feature is necessary in the design of aircraft avionics in particular to assure system reliability. Cooling of components by this means necessitates a number of compromises to the overall system. These compromises include: high pressure drop; uniformity of component form factors; placing the components containing the integrated circuits further apart on the circuit cards; increasing the distance between circuit cards; and increasing the volume and velocity of cooling air directed over the components, which increase requires special considerations in the design of the housings containing the circuit cards and in the mechanical systems for delivering the cooling air.
Increases in the sophistication of electronic systems has brought about denser packaging of electonic components with attendant increases in power density and total card power. This has brought about the evolution of another technique which is a further conventional approach to cooling of card-mounted electronic components. This technique is to use solid metal thermal mounting cards or plates which conduct the heat dissipated by electronic components to a heat sink (cold plate) disposed at the edge of each card. Such an approach, however, results in a large thermal resistance from the component mounting surface to the heat sink, which causes high component temperatures. In an effort to mitigate this problem with metal cards, the prior art has turned to heat pipe technology, a technology with which the subject invention is concerned.
3. Description of the Prior Art
The subject invention is a solid metal circuit card having a heat pipe on edges thereof for dissipating heat by electronic components thereon to a heat sink. Heat pipes per se are, of course, well known, as are solid metal circuit cards or boards for mounting electronic components. In the prior art also there are teachings of metal circuit cards incorporating therein heat pipes for dissipating the heat generated in operation by electronic components mounted on the cards. Constructions of this type are disclosed by K. T. Feldman, Jr., in U.S. Pat. No. 3,613,778; C. J. Feldmanis in U.S. Pat. No. 3,651,865; R. G. McCready in U.S. Pat. No. 4,019,098; and L. A. Nelson et al. in U.S. Pat. No. 4,118,756.
In these prior art designs, it is an object to mount the electronic components directly over heat pipes incorporated in the body of the circuit card or board itself. Because of the danger of puncturing the heat pipe, it thus is not feasible to drill holes in the mounting surface of the board for the mounting of components thereon. For this reason it is thus necessary in most of these designs to bond or weld the electronic components to the surface of the board. As it is not feasible to drill holes in the metal card to mount components by the conventional wire wrap method, this inexpensive, rapid, efficient technique, therefore, is not readily available for use with the prior art heat-pipe cooled circuit cards. McCready in the prior art teaches an alternate component mounting method on a heat-pipe cooled circuit card. In McCready, the terminal pins of the circuit are fixed in the circuit card with the ends thereof projecting normal to the mounting surface and the connector pins of the component are bonded to the terminal pins with the tension of the connection so made holding the component against the surface of the circuit board in what is hoped to be a good heat transfer relationship.
It will be appreciated that the incorporation of heat pipes in the body of the circuit card thus makes it difficult to utilize effective, inexpensive conventional component mounting techniques and also the circuit designer is inhibited in the placement of components on the card. It is also seen that the interchangeability of these prior art circuit cards with pure conduction and air-over-component integrated rack designs is degraded by the alteration of the circuit card form and fit factor due to the incorporation of heat pipes in the body of these prior art circuit cards.